The long-term goal of the proposed research is to characterize the nature of positional memory in embryonic and regenerating limbs. The research is based upon the hypothesis that from positional cues the cells of a developing limb are able to recognize their relative position within the limb field and, on the basis of this information, differentiate accordingly. I am hypothesizing that limb cells of animals (e.g. unrodele amphibians) that can regenerate limbs have a stable, long-term positional memory whereas embryonic limb cells of animals (e.g. bird or mammal) that cannot regenerate limbs posses a short-term, less stable or less expressible memory of their positions. The specific aims of this proposed research are 1) to develop methods for preserving positional memory in vitro and to develop in vivo and to develop in vivo assay methods for demonstrating the presence or absence of positional memory in the cultured tissues and 2) to investigate the ability of cells and tissues grown outside the limb field to retain their positional memory. The proposed research wil be conducted upon avian embryos and salamanders, and will involve studies on pattern formation and morphogenesis of both embryonic and regenerating limbs. The principal techniques will consist of in vivo grafting operations, cell and tissue culture, and morphological methods at the light and electron microscokpic level. The results of this research are expected to shed light on mechanisms of normal and abnormal limb development as well as mechanisms that may be related to the ability or lack of ability of limbs to regenerate.